/Engine/Source/Runtime/Engine/Classes/PhysicsEngine/ConstraintTypes.h
struct FConstraintBaseParams
uint8:  1
bSoftConstraint
Whether we want to use a soft constraint (spring).
float
ContactDistance
Determines how close to the limit we have to get before turning the joint on.
float
Damping
Damping of the soft constraint. Only used when Soft Constraint is on.
float
Restitution
Controls the amount of bounce when the constraint is violated.
float
Stiffness
Stiffness of the soft constraint. Only used when Soft Constraint is on.